A major portion of blood supply to the brain hemispheres is by two arteries, referred to as common carotid arteries (CCA), each of which branches off, or bifurcates as the term is at times used, into a so-called internal carotid artery (ICA) and an external carotid artery (ECA). Blood to the brain stem is supplied by two vertebral arteries.
Cerebrovascular diseases are considered among the leading causes of mortality and morbidity in the modern age. Strokes denote an abrupt impairment of brain function caused by pathologic changes occurring in blood vessels. The main cause of strokes is insufficient blood flow to the brain (referred to as “an ischemic stroke”) which are about 80% of stroke cases.
Ischemic strokes are caused by sudden occlusion of an artery supplying blood to the brain. Occlusion or partial occlusion (stenosis) are the result of diseases of the arterial wall. Arterial atherosclerosis is by far the most common arterial disorder, and when complicated by thrombosis or embolism it is the most frequent cause of cerebral ischemia and infarction, eventually causing the cerebral stroke.
Cardioembolism causes about 15%-20% of all strokes. Stroke caused by heart disease is primarily due to embolism of thrombotic material forming on the atrial or ventricular wall or the left heart valve. These thrombi then detach and embolize into the arterial circulation. Emboli large enough can occlude large arteries in the brain territory and cause strokes.
Cardiogenetic cerebral embolism is presumed to have occurred when cardiac arrhythmia or structural abnormalities are found or known to be present. The most common cause of cardioembolic stroke is nonrheumatic (non-valvular) arterial fibrillation (AF), myocardial infarction, prothetic valves, rheumatic heart disease (RHD) and ischemic cardiomyopathy.
Such disorders are currently treated in different ways such as by drug management, surgery (carotid endarterectomy) in case of occlusive disease, or carotid angioplasty and carotid stents.
While endarterectomy, angioplasty and carotid stenting are procedures targeting at reopening the occluded artery, they do not prevent progression of new plaque (restenosis). Furthermore, embolisms from the new forming plaque in the internal carotid artery (with or without a stent implanted therein) can occlude smaller arteries in the brain and cause strokes. Even more so, the above treatment methods do not prevent proximal embolic sources, i.e. embolus formed at remote sites heart and ascending aorta) to pass through the reopened stenosis in the carotid and occlude smaller arteries in the brain.
It will also be appreciated that endarterectomy is not suitable for intracarnial arteries or in the vertebrobasilar system since these arteries are positioned within unacceptable environment (brain tissue, bone tissue) or are too small in diameter.
Introducing filtering means into blood vessels, in particular into veins, has been known for some time. However, filtering devices known in the art are generally of a complex design, which renders such devices unsuitable for implantation with carotid arteries, and unsuitable for handling fine embolic material. However, when considering the possible cerebral effects of even fine embolic material occluding an artery supplying blood to the brain, the consequences may be fatal or may cause irreversible brain damage.
However, in light of the short period of time during which brain tissue can survive without blood supply, there is significant importance to providing suitable means for preventing even small embolic material from entering the internal carotid artery, so as to avoid brain damage.
A drawback of prior art filtering means is their tendency to become clogged. On the one hand, in order to provide efficient filtering means, the filter should be of fine mesh. On the other hand, a fine mesh has a higher tendency toward, and risk of occlusion.
It should also be noted that the flow ratio between the ICA and the ECA is about 4:1. This ratio also reflects the much higher risk of embolic material flowing into the ICA.
It is thus an object of the present invention to provide an implantable deflecting device suitable to be positioned within a blood vessel supplying blood to the brain, and further suitable to deflect embolic material that would have flown into the internal carotid artery, into the external carotid artery, thereby preventing the entry of said embolic material into the internal carotid artery, and thus preventing extracranial embolus to occlude small intercranial arteries in the brain.
It is another object of the invention to provide a method for preventing conditions associated with embolic material.
Other objects of the invention will become apparent as the description proceeds.